When a diesel engine is used in a mine, either on a railed vehicle, suspended monorail, or for a standard tractor, loader, or when it is used in close proximity to people and to explosive gases and the like, it is necessary to provide it with certain safety features. The exhaust gases must normally be cooled considerably, to at most about 70.degree. C., before being released to the surrounding air. Furthermore in a mine it is essential to avoid the ignition of surrounding explosive gases, either by suckihg them into the engine intake and having them flash back or by igniting them directly with the engine exhaust. Although a properly tuned diesel engine will generate minimal pollutants except for easy-to-filter particulates, it is extremely difficult to dissipate the large amount of heat generated in such a high-compression machine.
In British Pat. Nos. 549,398 filed July 23, 1942 by A. Flatt and 670,732 filed June 23, 1950 by F. Staddon plate-type flame arresters are described which each have a stack of plates that form a plurality of relatively circuitous passages of a width of about 0.8 mm, which is large enough to pass particulate matter without clogging. Any spark or flame in the gas passing through such a device, whether going into the intake manifold of the engine or coming from the exhaust manifold thereof, will be cooled and quenched.
British Pat. No. 903,493 filed May 1, 1961 by D. Brown describes an exhaust pipe which is jacketed so that a liquid coolant can flow through it to cool the exhaust gases therein. In addition some of water is sprayed directly into the flow of exhaust gas to scrub and cool it. The thus cooled gases are then passed through a flame arrester and mixed with ambient air prior to discharge to the atmosphere. Thus the temperature of the exhaust gases is reduced greatly and any harmful constituents of the gas are eliminated and/or attenuated. Another such jacketed exhaust pipe is described in British Pat. No. 1,303,336 filed Sept. 17, 1971 by N. Parfitt.
The system of British Pat. No. 1,037,339 filed Aug. 27, 1964 by H. Hammitzsch et al aims at reducing water consumption in a system such as described immediately above by cooling the exhaust gases wholly by indirect heat exchange. To this end the exhaust gases pass meander-fashion through a succession of individual tube assemblies enclosed in a housing filled with a liquid coolant. By the time the gas has traversed all these tube assemblies its temperature is reduced to a safe level. In addition the tube assemblies are set up with manifolds of large flow cross section to strip particles from the gas stream being cooled.
A complex cooling and control system is described in British Pat. No. 1,246,888 filed May 12, 1969 by Envirotech Corporation. This arrangement employs the latent heat of evaporation of water that is injected into the exiting exhaust-gas stream to cool it. The flow of water to the injectors is controlled in accordance with various engine operating parameters. Similarly U.S. Pat. No. 3,621,652 filed July 2, 1970 by J. Demaree passes the exhaust gases through a pair of chambers. In the first the gas gives up heat and in the second it is cooled directly by spraying water into it. Thus the cooling effect in the second chamber is applied to the upstream gases.
In U.S. Pat. No. 3,831,377 filed July 24, 1972 by A. Morin a separate radiator and coolant circuit is used to chill the exhaust gases so much that many harmful constituents are condensed out of them. In addition the lighter volatile phase is separated out and fed back to the intake manifold.
All of these systems are relatively complex. In addition few of them reliably provide the level of explosion protection needed on a diesel engine used in a mine or other dangerous location.
In my above-cited copending patent application I further describe a diesel engine having a fresh-air intake, an exhaust-gas output, and a cooling system in which a liquid coolant is circulated. This system is provided with an antiexplosion system having an intake flame arrester in the intake and a jacketed exhaust-pipe section connected to the output and receiving exhaust gases therethrough from the engine. The cooling system is connected to the jacketed exhaust-pipe section to cool same and to cool the exhaust gases therein by indirect heat exchange with the coolant. An exhaust-gas heat exchanger is connected through the jacketed pipe section to the output. The cooling system is also connected to the heat exchanger to cool the exhaust gases therein by indirect heat exchange with the coolant. An output flame arrester is connected via another exhaust-pipe section to the heat exchanger for conducting cooled exhaust gas from the exchanger to the arrester.
With such an arrangement the exhaust-gas cooling is integrated with the engine, and there is no need for a continually replenished external water supply. The mess made by engines where water is injected right into the exhaust gases is completely eliminated. In addition the pressure-related problems of the water-injection systems are completely avoided as well of course as the necessity of providing for a mobile water supply either connected to or mounted on the vehicle incorporating the engine system.
This arrangement, which is also generally described in British Pat. No. 2,093,119, functions well, but is susceptible of refinement.